The present invention relates generally to electronic video game units having a digital processor which operates to display a video game on a television receiver in accordance with a set of instructions stored in a removable memory element.
Video game units, particularly those intended for use in the home, are normally adapted for use with conventional television receivers. Such video game units typically include microprocessor-based circuitry which electronically generates signals corresponding to the various backgrounds, moving characters and sound effects which make up a particular game. Within the game unit the microprocessor generated signals modulate a radio-frequency (RF) carrier to produce an RF output signal at a selected frequency channel similar to the signal transmitted by a conventional television broadcast station. When a signal thus generated by the video game unit is applied to the input terminals of a conventional television receiver tuned to the selected channel, the microprocessor generated signals appear as a game display on the television screen and corresponding sound effects are produced through the television receiver audio circuit.
Typically, in conventional home video game units different digital game programs can be provided to the microprocessor to create different game formats. Such instructions are contained in a video game memory element contained within a separate cartridge which can be removably inserted in the video game unit.
If a removable cartridge is inserted in a video game unit while the game unit is powered, it is possible for the resulting power surges and static discharges to damage the voltage sensitive digital circuitry of both the video game unit and the cartridge. In order to avoid the possibility of such damage, it is customary to instruct the user to disconnect power to the video game unit before a cartridge is inserted into or removed from the unit. However, when power is thus removed from the video game unit, the RF signal the unit normally produces is no longer generated. As modern television receivers are equipped with automatic gain control circuitry, the loss of the RF signal at the input terminal of the receiver causes the gain of the tuner and intermediate frequency amplifiers of the receiver to greatly increase. When this occurs, noise inherent in the tuner and intermediate frequency stages of the television receiver is greatly amplified and appears at the output of the receiver in the form of a bright video display and a loud hissing noise, which users often find objectionable. This causes some users to decrease the volume setting of the television receiver prior to removing power from the video game unit. Other users are induced to attempt changing cartridges while power remains applied to the game unit. At best, this results in inconvenience to the user, and at worst, the circuitry of the game unit and cartridge can be electrically damaged.
In view of the foregoing, it will be appreciated that to provide a video game unit wherein power is removed from the sensitive digital circuitry of the unit as game cartridges are interchanged. without resulting in the production of objectionable output by the television receiver, would constitute a marked improvement over conventional video game units.